I wasn't quite sure what to expect with this book. It appeared in a list of recommendations based on some of my recent mental hospital-heavy choices, and the description sounded intriguing. The book had its ups and downs, but on the whole it's an interesting read.
The story is that of Dr. Charles Marsh, a psychiatrist working in an asylum in northern Wisconsin. His first patient is a young girl who had a bad experience out on one of the islands near the asylum. When Dr. Marsh first arrives, she is beginning to have visions of "shadows" that are coming out of the walls and threatening her. Dr. Marsh of course starts out believing that these are mere hallucinations, but soon he is forced to consider other possibilities. As this is going on, it also begins to spread to some of his other patients. Dr. Marsh takes it on himself to document what is happening and what it all might mean.
The book is written in an epistolary style--the story is told via Dr. Marsh's notes, transcripts of his sessions with patients, historical documents, newspaper articles, and various other bits of paper. It's a really interesting way of doing things, though in the middle the story seems to drag a big before winding up to its disturbing conclusion. The format does keep things moving along surprisingly well, by cutting back and forth between the different patients and Dr. Marsh's interpretation of what might be occurring.
This isn't a book for people who like their scares to be gory, violent, or graphic. In this case it is more about atmosphere and creepiness. It's also just interesting to read because the format is one I don't see very often, though it seems to work quite well for this style of book. I'd give this a conditional recommendation--the style and subject matter are not for everyone, but some may enjoy it.